1. Field of the Invention
The present invention relates to an antenna, and more particularly to a broadband antenna that has multiple radiation conductors connected in series as a conductor string.
2. Description of Related Art
Wireless Communication technologies develop rapidly in recently years and various wireless products are marketed popularly. One of most important components in wireless product is an antenna. The design of the antenna requires stricter criteria than the past in size and performance aspects. Taking account of the appearance and size of wireless products, miniature antennas for those products are necessary. Accordingly, the monopole antenna utilizing a metallic ground plane to replace a negative radiator is developed. The monopoly antenna achieves superior radiation effects with a shorter length, i.e. a half of that of a dipole antenna. Subsequent to the monopole antenna, fabricators develop a folded monopole antenna with bent metallic strips to further miniature the size of the antenna and solve the problem of blind area.
With reference to FIG. 1, an antenna matching circuit is disclosed in U.S. Pat. No. 6,081,242 and comprises a printed circuit board (10) with a surface (101), a first inductor (102), a capacitor (103), a second inductor (104), a connection pad (105) and a ground plane (106). The connection pad (105) is formed on the surface of the printed circuit board (10) and coupled to the first inductor (102). The capacitor (103) is formed between the first inductor (102) and the second inductor (104). The second inductor (104) is further coupled to the ground plane (106). With zigzag traces constituting the inductors (102)(104), the antenna matching circuit has higher coupling efficiency and a shorter length. However, such an antenna matching circuit does not support multi level resonance and its impedance bandwidth is also limited. Further, the input impedance of the antenna matching circuit cannot be adjusted to achieve required impedance match.
To overcome the shortcomings, the present invention provides a broadband antenna to mitigate or obviate the aforementioned problems.